Tag: dxf

So when dealing with ‘world’ coordinates in a point cloud, sometimes things just don’t work too well. I thought I had this all solved recently by using the DXF, Center-to-Center, Acquire Coordinates workflow. However, I discovered that somewhere along the line, Revit still does break down with the large coordinates. I think this is happening in between Recap and the Revit point cloud rendering engine. I was getting something that looked like this:

As you can see, the shared coordinate system is very large. In this situation, you can’t even move the point cloud into the correct location in Revit, it jumps in large increments when moving. Interestingly, Navisworks and AutoCAD both handle these large coordinates ok – appending the same data does not have the error shown above. So…

How do we fix this and make Revit happy?

Basically, we do a temporary truncation of the source data, get it into Revit, and then reinstate the appropriate coordinate system.

To truncate the data, have a look at your source point cloud information. In my case, I could identify 4 leading digits for the X and Y coordinates that were not significant:

Using EmEditor (which handles large text files very well), and its Vertical Selection feature, I was able to delete the 2781 and 6181 digits from my source data.

In effect, this transformed everything by 278100m and 6121000m. Keep these numbers in mind for future reference…

Ok, with the simplified source data in hand, I followed these steps:

Index a new RCP in Recap using the simplified data

Open surveyor DXF file in AutoCAD and manually Move all the geometry. Move the objects by the values above (278100, 6121000) towards the origin. Save As – a new DWG file with modified coordinates.

Link this modified DWG into Revit, Center-to-Center

Acquire Coordinates from it

Link the Point Cloud RCP By Shared Coordinates

Everything lines up now that the large coordinate shift error has been avoided!

Link in the original DXF and align it with the modified temporary DWG we were using

You may need to temporarily neutralize coordinates (here or here), and…

Now you can Acquire Coordinates from the original DXF and you will have reinstated the ‘world coordinates’, but the Revit point cloud rendering engine is now much happier.

I thought that most of this was ‘easy’ and solved now, but it was more of a challenge than I expected. I received aASC file from a survey in XYZRGB format, which looks like this:

Those XYZ values are Metres (or Meters if you are in US) in the MGA 94 coordinate system. I also received aDXF file with the same World coordinates, and project related gridlines so I could relate the pointcloudto our Revit models.

I tried getting the MGA Shared Coordinates right inRevit, and then linking an RCP or RCS from Recap ‘by Shared Coordinates‘, but I didn’t have much joy.

Here is the workflow that worked for me…

Getting the right Shared CoordinatesinRevit

Start a new, blank Revit model

Link the DXF Centre-to-Centre (this is best way to deal with huge coordinates)

Acquire Coordinates from it

Save your Revit file. You now have the right World coordinates, and a project grid relationship.

Importing the PointCloud by Shared Coordinates

Open Recap and import the data. For the ASC dataabove, on the import settings I used ‘Advanced’, and chose the text columns XYZRGB. I also set the coordinate system.

Export to PCG. Sounds weird, I know. But PCG is a nice reliable container that supports colours.

We often have to deal with data that hasn’t always “lived” in our CAD, BIM or Revit world. Take a hand sketch, for example – how can you get that into a format that can easily be used in AutoCAD or Revit? Some PDFs have vector information, which I have described how to access before. But the below workflow takes it one step further – how to get any raster image into a vector format, using a few free tools.

Sometimes you will have access to a PDF file, but not to the original DWG. Is there any way you can get the base vector data, such as lines and arcs, out of the PDF and back into a DWG? Yes, there is – and it’s free.

Let’s say you have AutoCAD file of unknown origin, and it has some wacky or imprecise units (like the distance between two walls is 8250.092234897). What you need to do is reduce the precision, such that all the decimal points get ‘chopped off’.

To do this:

Open the offending DWG in AutoCAD.

‘Save As’ and choose a DXF format.

Go to Tools menu – Options (see below)

Choose DXF Options, ASCII Format and set the ‘Decimal Places of Accuracy’ to the desired value (choosing 0 will remove all decimal places):

Hit Save.

I recommend that you now open the DXF file you saved, and then resave it as a DWG file.Now you can insert your file into Revit, and you won’t have to deal with imprecise units.Please note that this process may result in some ’rounding off’ of values – you may want to double check the resulting file.